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26X 


30X 


28X 


32X 


I     i 


B 

Stalls 
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r  une 
Image 


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)S 


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empreinte. 

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symbole  V  signifie  "FIN". 

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de  Tangle  supArieur  gauche,  de  gauche  d  droite. 
et  de  haut  en  bas,  en  prenant  le  nombre 
d'imagas  nicessaire.  Les  diagrammes  suivants 
iilustrent  la  m^thode. 


errata 
to 


t  pelure, 
on  d 


n 

32X 


i 


i 


1 

2 

3 

1 

2 

3 

4 

5 

6 

lU 


I 


On  the  Use  of  the  Interferometer  in  the  Study 
of  Electric  Waves 


*■   ■ 

SUBMIISTtD  TO  THK  FaCULT«8  OF  THE  GRADUATE  SCHOOLS 

OF  Arts,  Literature,  and  Soence,  in  Candi- 
dacy FOR  THE  Degree  of 

DOCTOR  OF  PHILOSOPHY 
{Dipartmmtof  Phyna") 


BY 

GORDON  FERRIE  HULL 


(l^rinted  item  die  Phtoigal  Rbvikw,  VoL  V.,  Na  28,  OctolKr,  «897 ) 


r'^, 


CHICAGO,  MAY   i,  1»97 


•=-§■%•- r* 


'*■ 


r^  ~-  -  > 


il.^^a^V~  .^.i*. 


-H- 


iA.c  ■      . . . .   iv-iSf  ■~r^- 


THE   PHYSICAL  REVIEW. 

'■A  JOURNAL  OF  EXPERIMENTAL  AND   THEORETICAL  PHYSICS. 

CONDUCTBO  BY 
BDWAKD  L.  mCHOU, 

■busst  mibritt,  and  fbbdkkick  bbdbll. 


Beginning  with  Volume  V.  (July-December,  1897),  two  vol- 
umes of  The  Physical  Review  will  be  published  annually,  these 
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Volumes  I.-IV.  of  The  Physical  Review  are  annnal  volumes, 
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PUBLISHED  FOR  CORNELL  XJNIVERSITY. 

THE  MACMILLAN  COMPANY,  NEW  YORK. 


Cbc  "lanivcrsitv)  of  Cbicaoo 

lofspKI)    I'.Y    .imiN    1>.    Kill  K  I'll  M.I  K 


On  the  Use  of  the  Interferometer  in  the  Stiidv 
of  Electric  Waves 


A    DISSERTATION 

SniMirTKi)   1(1   riiK  FAeri/riF.s  ok  thk  (Ikadia  ik  Smooi- 
oK  Arts,  LriKKATiRK,   and  Sliknli:,   in  Candi- 
dacy I'OK    riiK   I)k(;i<kk.  ok 


DOCTOR  Ol'  PHILOSOPHY 

{/),fay!iih-iit  of  I'/iysiis) 


'»« «• 


HY 


GORDON    FKRRIK    HULL 


(Reprinted  from  the  rilYSUAl.  Rkview,  Vol.  V.,  Xo.  2.S,  i  idolier,  i.S(j7  ) 


CHICAGO,    MAY    I,    1897 


f4 


-i 
r 

iJ 


p. 


^J.^>^-/  ^c     , 


ox     Till':    L'Sl".    ol'   Tl 
STUDY   01 


■:  i\ri:Ri-i:R()Mi:ri':R  in    r 
i:li:ctric  \v.\vi:s. 

liv    (i.    I',     ill  II. 


OlTMNi:. 

1.  Introduction. — Use  of  tlic  intcrfLTonictcr  in  the  study  of  lij^ht. 

2.  Historical  statrnicnt. — .Xnalo^y  between  iiijht  and  electric  radia- 

tion not  complete.  Work  of  .Saiasin  and  de  la  Rive,  .  .  .  for 
Hertzian  apparatus  pro\in_L^r  that  tlie  \va\e-lenj4th  nieasuretl 
depends  on  the  recei\er.  Is  the  ratiiation  from  a  I  lert/ian 
vibrator  simi)le  or  complex  ?  I'",.\i)eriments  anil  theory  dealiiiLC 
with  this  point.      lieariiiL,^  of  this  theor\-  in  our  experiments. 

3.  .Apparatus. — Interferometer;    conditions  ^a)verninj;  choice  of  \i- 

brator  and  receiver ;  sensitiveness  ;  absence  of  diffracted  aiul 
scattered  radiation  ;  preliminary  observations. 

4.  Measurement  of  /.. — DeL;rce  of  accuracy. 

5.  Ivstimation  of  " />'  "  from  the  interference  curve. — Proof  that  this 

does  not  ^^ive  the  loj^arithmic  decrement  of  the  vibrator,  as  has 
been  suppo.sed.      Comparison  of  experiment  with  theory. 

6.  Influence  of  receiver  upon  the  interference  curve. — Inference  as 

to  the  period  and  dampin<,r  coefficient  of  our  receiver. 

7.  Dependence  of  ?.  upon  vibrator. — No  agreement  between  \alues 

of  /  found  by  other  observ.    ■  for  vibrators  similar  to  our  own. 

8.  Determination  of  /i. — Degre.     .  accuracy.      Conclu.sion. 

I.  Use  of  tiik  Interferometer  in  the  Studv  of  Licht. 
The  interferometer,  as  a  special  form  of  refractometer  has  been 
called  by  Professor  Michelson,  has  been  found  to  be  a  very-  power- 
ful instrument  in  the  study  of  light.  By  its  mean.s  the  nature  and 
wave-length  of  the  radiation  from  a  source  and  the  index  of  refrac- 
tion of  a  transparent  medium  have  been  found  with  the  greatest 
accurac)'.  It  is  true  that  a  grating  or  prism  spectroscope  must  be 
used  for  the  study  of  complex  light,  but  for  comparatively  simple 


/.   //Y  //, 


[VmI,    V 


radi.iliini  tlu' inltrtlniiiKtrr  pusscsscs  afar  ^naUr  pouir  of  analysis. 
It  was  witli  the  oliji'ct  of  constructing  an  intcrfcronictiT  for  electric 
waves  and  of  nsinj,'  it  in  tlnir  study  liiat  tliis  ivse  mtIi  was  nndrr- 
takiii. 

2.  1  Iciv  it  may  he  well  to  point  out  that  electrical  and  lij^dit  oscil- 
lations differ  in  an  important  respect.  The  hreadth  of  a  spictral 
line  of  a  liomoj;enei)Us  ^as  has  been  accounteil  for  upon  various 
assumptions  amon;^  which  is  the  one  that  the  oscillations  of  the 
molecules  of  the  ^as  ^raduidly  die  down  owinj^^  to  its  communi- 
cating^ ener^)'  to  the  surrountlin^  medimn,  or  to  other  causes. 
l'",xperiments,  however,  have  failed  to  \erify  this  assumption.'  In 
the  case  of  electrical  radiation,  cm  the  other  hand,  theor\'  indicates 
and  eNperimeiit  proves  that  the  oscillations  are  alwaj's  damped. 

Another  difference  is  in  the  apparatus  used  for  detecting  thi'  radi.i- 
tion  in  the  tui)  cases.  I'"or  li^dit,  tlu'  eye  is  the  usual  tletector. 
'rhoui;h  it  is  sensitive  for  radiation  lyin^  within  a  very  small  range, 
it  has  no  periiul  of  its  own  and  does  not  possess  the  power  of  influ- 
eiicin^f  the  measured  wave-length.  That  electrical  receivers,  as  a 
rule,  have  this  power  has  been  pro\ed  by  the  experiments  of  Sara- 
sin  antl  lie  la  Rive,"  Klemencic  antl  Czarmak,'  and  (|uite  recently 
b\-  those  of  Wiedeburg.'  In  fact,  for  the  different  forms  of  I  lertzian 
vibrators  and  receivers  used  by  these  ph\'sicists,  the  wave-length 
measureil  depemled  almost  entirely  upon  the  receiver. 

The  explanatioi;  of  this  fact  led  to  the  important  cjuestion  whether 
the. radiation  from  a  Hertzian  vibrator  is  simple  or  complex.  Ui)on 
this  point  opinions  have  differed.  I'rom  the  phenomenon  of  multi- 
ple-resonance as  discovered  by  Sarasin  and  de  la  Rive-  and  Klem- 
encic and  Czarmak'  many  physicists  were  led  to  the  conclusion 
that  the  radiation  is  comi)lex.  The  experiment  of  Zehnder''  show- 
ing that  the  rays  of  electric  force  are  analyzed  by  a  grating  into  a 
spectrum  pointed  in  the  same  direction,  while  Garbasso  and  Asch- 
kinass''  found  that  rays,  in   passing  through  a  prism  made  up  of 

'A.  A.  Mii'liclson,  .\stiophysital  Imirii.'il,  ]>.  251,  Xnvcmlicr,  iSyS. 

2  Sarasin  aiul  dc  la  Rivo,  t'nmpt.  KlikI.,  1 1 5,  ]>.  439,  1892. 

!<  Klciuciicic  and  C/ariuak,  Wiod.  .\iin.,  XOl.  $'>,  1S9J. 

< WicdclniiK,  NVied.  .\iin.,  \ol.  59,  p.  496,  1S96. 

''•/clindor,  Wicd.  Ann.,  VdI.  5,5,  p.  172,  1894. 

oGaiiiasso  and  Asclikina.ss,  Wicd.  .\nii.,  Vol.  53,  p.  534,  1S94. 


4l 


r.VA  ('/•   /AV/A7/ A'(',l//7/ A'. 


^;lass  pl.itcs  up'ii  uhicli  \\\\v  pastcil  strips  of  tiiituil,  an'  disporsfc! 
ami  coiicliidicl  lliat  rays  of  ckctric  fi>\w  iiia>'  \n-  lonsidi  inl  imt 
necessarily  as  iiiDiiotlirdniatic  hut,  with  the  sanu'  jiistifuMtidii  .is  in 
the  case  of  li^lit,  as  c  Jiiipositc,  (  )ii  tlie  other  h.md  HJimUiu's' 
iisJM^r  I.i'eher's  arrail^'enieiit  •'  attemptid  topicve  that  tlie  radiation 
is  (hic  to  a  simple  clamjied  oscillation  of  tlic  form  . /,  "•  sin  {iiZ  +  a'). 
Tile  theory  of  his  nuthoil,  u  hicli  iliffered  from  the  latir  work  of 
KIcmeiicic  ami  Czarmak  chictly  in  tiiis  that  he  used  waves  aloiin 
wires,  uhili'  they  useil  waves  in  air  is  as  follows  :  .Assuming'  that  the 
oscillations  are  of  the  form  ./,""' sin  (t/,  he  finds  the  effeet  upon  the 
receiver  of  two  infniite  tr.iins  of  waves,  one  of  which  is  direct 
from  the  vibrator  anil  the  other  rellected  from  the  ends  of  the  wires. 
This  effect  (usin^  notation  and  limits  of  inte|^n-ation  to  suit  our 
experiment)  is  j^iven  by 

./=  C' J<--"'.sin-,?/,//4-  ['^^  [-h-'siv  ,//+./,-"("■'"'  .sin  a  i/+  ~'\Y 

.1-  I         "■'•  .IV 

=       1 1  -ft'  -   cos  2a    I. 


In  lijerknes'  experiment  .r  was  the  distance  of  the  receiver  from  the 
end  of  the  wires  ;  in  ourexperiments  it  is  the  distance  of  a  mirror  from 
the  "  zero  position  "  ;  in  both  cases  2.ris  the  total  difference  in  path  of 
the  two  trains  of  waves.  Thus  the  curve  wiiosc  ordinates  are  i)ro- 
porlional  to  the  intensity  of  the  electrical  radiation  for  a  jjoinl  v\  hose 
abscissa  is  .r  ,  is  leaving  out  a  constant,  a  tlamped  cosine  curve, 
It  was  found  that  the  experimental  ai,n-eed  fairly  well  with  tlie  theo- 
retical curve.  It  was  therefore  concluded  that  the  oscillations  fol- 
lowed the  law  assumed. 

This  conclusion  is  open  to  two  possible  criticisms  which  are  su^^- 
ge.sted  by  the  questions  :  first,  may  not  the  wires  with  their  terminal 
plates  or  the  receiver  e.xercise  a  selective  action  on  the  radiation,  and 
second  may  not  the  interference  curve  be  obtained  assuming;  an- 
other iaw  for  the  oscillations.  Indeed  ]5jerknes  found  that  the 
inteiference  curve  was  infliienced  by  the  chanj^e  of  the  distances 
between  the  plates  of  the  vibrator  and  the  terminal  plates  of  the 

'  lijoiknes,  NVicd.  .Ann.,  Vol.  44,  ji,  51J,  iS(,i. 
^I.echcr,  Wicd.  Ann.,  Vol.  41,  \i.  S50,  lSi,o. 


G.  /•;  ///•// 


IV.. I..  V. 


wires — tli.it  ,is  tliis  ilistancc  iiicivaNtil  tin.'  u,i\rs  uiii.'  imt  su  i,i|)- 
i(ll\-  (l.miprd  hut  were  laintt-T — a  result  wliich  aj^rirs  uitli  tlu' 
thc(iry  tliat  the  mnie  teil)le  llie  lailiatimi  the  less  rapid  is  its  de- 
cay. I'ri)l),il)l)-  the  uiris  were  too  Inn^'  to  atlect  the  result  hut  that 
is  a  point  uhieh  in  ^eiier.d  slmuld  he  considered. 

The  results  ohtaiiied  h)'  .Sarasin  ;iiul  de  l.»  Ri\e  ami  the  other 
ph)sicists  named  .ihow,  indicitiii^;  th.it  the  radi.ition  is  complex, 
m.iy  he  .iceounted  for  h_\  .issiimin^f  th.it  the  oscill.itions  are  simple 
■md  d.imped  .iiid  th.il  the  receiver  h.is  ,i  piriod  of  its  oun  and  is 
conip.iratively  und.imped.  On  the  other  h.md,  lU'^lectiuj^  the  criti- 
cisms hroiiL;ht  forward,  it  would  he  diflicult  to  account  for  the  rej^'ii- 
l.irit)'  of  the  interference  curve  ohtainetl  !))•  Kjerknes  on  the  assump- 
tion that  the  radiation  is  complex.  On  the  whole  the  (piestion  has 
not  Ik  en  satisfactorily  settled.  We  are  justificil  in  expectini^^  that 
the  prohkni  may  he  approximatel)'  soUed  hy  means  of  the  inter- 
ferometer. 

The  ([iiestion  which  concerns  us  is  this — e'ven  if  electric  radiation 
is,  in  general,  suflicientl)-  simple  to  be  analyzed  hy  the  interferom- 
eter, how  shall  we  inter[)ret  the  interference  curve — is  its  form  influ- 
enced by  the  receiver?  The  latter  point  is  a  matter  for  experiment 
to  decide  in  the  case  of  the  receiver  u.sed. 

Xoti'. — The  theory  which  applies  here  is  rather  unsatisfactorj'. 
Assuming;  that  the  receiver,  when  no  outside  forces  act,  executes 
dampetl  pendulum  motions  and  th.it  the  oscillations  of  the  vibrator 
arc,  of  the  same  nature  wc  obtain  the  equation  : 

'J.+:-i  'J  +  (<i^>/'^)f =^i'-'"sin  {at+c) 

where  ^f  represents  the  potential  difference  between  the  parts  of  the 
recei\  er.  I,et  us  impose  the  conditions  9'=  ,  =0  when  t=o.  1  he 
solution  may  be  expressed  in  the  form — 


f=C  sin  I    ^    (+(■')  where 


.1- 


(rt-_/r)--f-(rt--//-)(«--^i-)  ■-  ^ 


Nn.  4,] 


is/-:  0/   A\7/.A7/.A('.I//. //.A'. 


I  4- cos  I 


-   ,,4./,  d"-^')'"  ^-[i-/>)i:n^{'i-/'y-('i-^ii^u\(.i-/'y)  + 


sill  I 


Tlif  in'tion  nil  the  R'c\i\ir  diir  to  tin-  t\v<i  trains  of  waws  is 

Tiiis  is  the  c(iiiati')ii  of  tln'  iiiti.'r(i.Tcncc  ciirw.  lUit  in  \ii\v  of  tlic 
iiiKxrtaint)-  of  tlii;  hjpoilusis  and  tlic  cinnpirxil)-  of  tlic  ii->ult,  it 
sclius  iiL-L-cllcss  to  expect  assistance  from  this  liii(>r\'. 

The  work  so  far  descrilxcl  was  pirformed  with  the  I  lert/ian  \ibra- 
tor  and  receivers.  I  am  not  aware  tliat  an)-  eorrespoiulin^  work  has 
been  done  witli  s|)heres  unless  it  is  that  of  l.anj^'  and  of  IJose."  I  .;i\v^ 
obtaineii  interference  effects  by  a  metliod  an.doj^nms  to  that  of 
(Jiiinke  in  sound.  But  it  seems  probai)le  tliat  retlectioiis  from  tiie 
tubes  to  which  tlie  raiiiation  was  led  would  obscure  the  effect.  Hose 
states  that  the  radiation  from  a  sphere  under  the  conditions  existinij  in 
his  experiment  {jives  a  ////<■  s|)ectruni  from  which  the  inference  is  to 
be  drawn  that  the  \ibrations  are  not  on!)-  simple  but  wry  sli^ditly 
damped,  lie  also  states  that  the  wave-lenjjths  measured  were  iiule- 
pendent  of  the  periodicity  of  the  receiver.  If  this  were  true  it  must 
ha\e  been  on  account  of  the  dead  beat  character  of  the  receiver — 
not  on  account  of  the  method  used. 

The  experiments  to  be  described  in  this  paper  will  show  (1)  that 
the  oscillation  due  to  electrical  disturbances  on  spherical  conductors 
are  for  the  most  part,  rather  liiyMy  damped  sine  functions,  (2)  that 
the  interference  curve  is  influenced  by  the  receiver — sometimes  to 
such  an  extent  as  to  change  the  apparent  wave-leiiyth. 

3.    Al'I'.AKATL'S. 

The  interference  device  shown  in  Fig.  i  was  patterned  after 
Michelson's  simple  but  effective  interferometer.  Radiation  coming 
from  the  parabolic  mirror  /^  falls  at  an  incidence  of  45°  on  a  sr/>ii- 
ratiitg  surface  S  which  reflects  part  to  M  and  transmits  the  rest 

'  Victor  von  Lang.     I'hil.  Mng.,  Kob.  1S96. 
«Iiose      IVoc.  Roy.  Soc,  Oct.  16,  1896. 


'I 


G.  /■:  HULL. 


[Vol..  V. 


which  {,foc.s  to  J/'.  Of  the  radiation  reflected  from  .1/  aiul  J/'  the 
parts  transmitted  and  rellected  by  .S"  fall  toj^^ether  upon  A'  (See  VVg. 
I ).  Difference  of  path  is  obtained  by  the  motion  of  one  or  both 
mirrors.  To  obtain  as  lart;e  an  effect  as  pos:-ible  in  A'  the  separat- 
ing surface  should  transmit  anil  rellect  one-half  of  the  radiation  I'all- 
\\v^  on  it.  For  this  purpose  there  were  pasted  on  a  piece  of  card- 
board, half  a  metre  st[uare,  strips  of  tin  foil  1x40  cms.  At  first  the 
adjacent  edges  of  two  neighboring  strips  were  one  centimeter  apart. 
Later  it  was  found  necessary  to  remove  every  alternate  strip,  mak- 
ing the  adjacent  eiiges  3  cms.  apart.'     The  reHection  and  transmis- 


Fig.  1. 

iThis  agrees  with  the  conclusion  of  Lord  Layleigh  deduced  from  theoiy,  viz.— a 
narrow  aperture  parallel  to  the  electric  '  Uirations  transmits  very  much  less  than  is  re- 
flected by  a  conductor  elongated  in  the  same  direction     Phil.  Mag.,  April,  1897,  p.  272. 


N".  4.] 


r.S'A    ('/•   l.\  II.KI  I.K'KME  I'EK. 


siini  powers  of  the  Ljratiiit;  wrrc  (ktiTiniiKi,!  1)\-  well -known  iiuaiis 
and  it  was  found  that  when  the  stiijjs  were  paralkl  to  tlie  ek'ctric 
oscillations,  this  <;ratiii|4  retlected  and  transmitted  about  half  of  the 
radiation  fillin;^  on  it. 

The  woollen  arms  t<ti  and  he  were  ;j;roo\ed  so  that  t!ie  supports  car- 
ryini;  the  mirrors  J/,  .)/'  and  /'  were  nio\al)le  aloni;  ,'(/,  (■/',  oc.  '1  he 
an^le  aob  was  approximately  a  ri^dit  ani;le  anal  the  mirrors  were 
placed  each  normal  to  its  arm  by  optical  means.  The  mirrors  M 
and  J/'  were  of  plate  ^lass  with  the  silvereil  surface  towards  o.  The 
parabolic  zinc  mirror /Miad  a  focal  leii^ijih  of  2.5  cm.,  a  hei;^ht  >>t 
40  cms.  and  an  aperture  of  30x40  cm.  As  it  was  intendeti  to  use 
wa\es  not  lon^^er  thm  10  cm.  tlie  ilimensions  of  J/ and  J/*  and  ■'! 
the  ajjcrturc  of /'were  lari;e  enouj^di  to  obviate  any  serious  diflrac- 
tion  effects.  The  focal  len^^th  of /' was  chosen  about  one-fourth  of 
the  wave-length  in  order  that  the  direct  and  reflected  waves  mi.;ht 
be  in  the  .same  phase.  But  as  the  radiation  was  too  stront^  (unless  the 
galvanometer  was  short  circuited)  this  precaution  was   unnecessar)-. 

The  arrangement  for  the  vibrator  usually  consisted  of  two  spheres 
connected  by  fine  wires  to  tlie  secondary  terminals  of  the  induction 
ct-il  and  sparking  to  each  other  in  oil.  ICach  sphere  was  screwed 
on  the  end  of  a  hard  rubber  rod  which  passed  through  a  rubber 
cork  and  this  was  inserted  in  a  glass  tube  about  10  cm.  long  and 
2.5  to  3  cm.  in  diameter.  This  tube  was  partiallj"  filled  with  oil — 
usually  vaseline  oil,  sometimes  paraffine  oil.  A  small  hole  blown 
in  the  side  of  the  tube  allowed  one,  by  rubbing  paper  between  the 
spheres,  to  partially  clean  them  without  removing  the  vibrator  from 
Its  position.  Righi's  arrangement'  was  also  used.  Four  hard  rub- 
ber rods  each  carr>'ing  a  s[)here,  were  attached  to  a  vertical  rod  in 
the  mirror  /'.  All  distances  were  adjustable.  The  tliird  sphere 
was  fastened  by  means  of  melted  wax  in  a  small  glass  cylinder  of  si:eh 
a  size  that  it  held  sufficient  oil  for  the  spark  gap  and  yet  allowed  the 
spheres  2  and  3  to  approach  until  their  surfaces  touched.  The  arl- 
\antage  of  this  arrangement  was  that  all  the  spark  gaps  could  be 
fairly  well  cleaned  by  paper  without  removing  the  spheres.  The 
rod  .//»  could  be  rotated  so  that  the  spheres  could  be  brought  out 
towards  the  aperture  of /'or  moved  back  to  the  focal  line. 

'  Kidii,  Mem.  del  K.  Acivl.  del  Se.  del  Insl.  di  l!nl(if;iiii,  T.  IV.,  1894. 


8 


c.  /.  ni  i.L. 


[V,,i..  V. 


The  rcccivLM-  chosen  for  this  experiment  must  fulfill  certain  condi- 
tions. It  must  be  sufficiently  sensitive  to  respcjnd  to  radiation 
reaching:  it  after  reflection  and  diffraction,  sufficiently  constant  to  ^mvc 
(luantit.ilive  results,  ami  as  we  desire  to  determine  the  nature  of  the 
radiation  it  should  respond  ecjually  well  to  waves  of  all  periods  sent 
out  b)-  the  vibrator.  Now  it  has  been  shown  that  1  lert/ian  receivers 
do  not  fulfill  this  last  condition.  It  was  thought  that  a  receiver 
which  responds  to  electric  wa\'es  of  periods  extending'  over  a  wide 
rant^e  would  measure  accurately  the  radiation  falling  on  it.  Having 
had  some  experience  in  the  use  of  the  colicrcr  (as  named  b)'  Lodge, 
though  the  name  seems  misleading)  we  thought  that  if  it  could  be 
made  constant  it  would  answer  our  purpose.  Consequently  we  used  a 
liranley  or  Lodge  receiver  consisting  of  small  nails  or  pieces  of  wire 
about  I  cm.  long,  in  a  glass  tube  i  5  or  20  cm.  long  and  filled  with  a 
lubricating  oil.  This  was  placed  in  the  focal  line  of  a  semi-circular 
zinc  retlector  of  .iperature  10x20  cm.  A  sheet  of  tin  foil  over  part 
of  the  aperture  served  to  shut  out,  if  neces.sary,  part  of  the  radiation. 
Lead  covered  wires  comiected  the  receiver  with  the  gaUanometer 
and  battery  which  were  enclosed  in  a  tin  box.  Thus,  with  the  cx- 
cei)tion  of  the  aperture  of  the  mirror,  the  whole  circuit  was  enclosed 
in  metal. 

In  order  to  make  the  deflections  small  enough  to  be  read,  the 
galvanometer,  a  simple  D'Arsonval,  was  short  circuited  by  a  resist- 
ance varying  from  one-fourth  to  one-half  of  an  ohm.  It  is  hardly 
necessary  to  state  that  in  finding  the  proper  grating  the  ordinary 
phenomena  of  polarized  radiation  were  observed.  For  example,  if 
the  receiver,  grating  and  \ibrator  were  placed  in  a  line,  with  the 
grating  immediately  in  front  of  the  receiver  and  its  strips  iiorizontal 
(perpendicular  to  the  vibrator),  almost  all  the  radiation  passed 
through.  If  the  strips  were  vertical  only  one-half  pas.sed  through. 
A  block  of  wood  with  its  fibres  vertical  transmitted  much  less  than 
it  did  when  its  fibres  were  horizontal. 

It  was  found  that  the  receiver  responded  nearly  as  well  when 
the  electric  oscillations  were  vertical  as  when  the>-  were  horizontal. 
In  this  respect,  therefore,  it  differs  from  the  Hertzian  receiver.  In 
order  that  the  diffracted  and  scattered  radiation  be  as  small  as  pos- 
sible, the  axis  of  the  mirror,  and  therefore,  also  the  vibrator,  were 


N...  4.] 


r.vA  or  ixri-Kir.ROMEi'ER. 


vertical,  for  in  this  pnsition  it  was  nut  luccssan-  to  have  metallic 
ends  in  the  mirror.  In  our  experiments  the  total  scattereil  radiation 
was  only  three  per  cent,  of  the  effect  when  there  was  zero  difference 
of  path  in  the  two  beams.  Considerini,'  the  faci  that  the  recei\er 
was  .sensitive  to  radiation  reachiiii;  it  in  all  directions,  whether 
from  the  air  or  from  the  wires  leadin;^^  to  the  ^^al\anonu■ter,  and  that 
it  responded  .sli^ditly  to  the  loni;  waves  of  the  induction  coil,  which 
was  not  enclosed  in  metal,  this  result  was  felt  to  be  satisfactor\-. 
A  small  induction  coil  with  an  ordinary  automatic  interruptor, 
operated  by  one  storage  cell,  completed  the  apparatus.  A  number 
of  interruptors  were  tried,  but  they  were  not  found  to  be  more  con- 
stant than  the  one  belont,nnL,'  to  the  C(.il,  and  were  more  complicated. 
Usually  the  key  was  closeil  for  about  one  .second.  Closini,'  it  for  a 
longer  time  did  not  increase  the  deflection,  but  onl\-  served  to 
destroy  the  sparkin;^  surfaces. 


\ 


4.    ]\Ik.\SL-I<I:MKNT  OK  /..       ImG.   2,  CtRVK    I. 

Thi.s  figure  was  found  by  taking  the  mean  of  four  deilections  for 
every  position  of  the  mirror  which  was  mo\ed  alwa\-s  in  one  direc- 
tion and  through  5  mm.  each  time.  After  So  or  100  readings  the 
vibrator  became  nearly  useless,  showing  a  deterioration  with  time. 
So  in  all  ob.servations  after  this  the  mirror  was  moved  forward  and 
back  :  c.  i^.,  to  determine  the  relative  readings  for  three  positions, 
a,  />,  c,  the  series  n  b  c  b  a  was  taken.  If  we  are  concerned  with 
the  wave-length  and  not  with  the  interference  cur\-e  it  is  necessary 
to  find  only  the  maxima  and  minima  positions.  But  the  accuracj- 
with  which  one  of  these  positions  can  be  determined  depends  on  the 
sharpness  of  the  curve  at  that  point.  Consecpiently  the  first  step  in 
the  determination  of  /  {or  even  of  ft)  is  to  roughly  plot  the  interfer- 
ence curve,  obser\-c  the  sharpness  of  the  maxima  and  minima  and 
choose  the  sharper  of  these  from  which  is  to  be  estimated  the 
desired  quantity. 

In  order  to  see  to  what  degree  of  accuracy  /  may  be  found,  the 
positions  of  four  successive  minima  were  observed.  The  following 
results  were  obtained,  the  numbers  referring  to  the  position  of  the 
mirror  on  the  scale 


10 

(;.  /••  J/L/.L. 

[Vol.. 





-  — 

Second        1 
behind. 

FirBt         !         First 
behind.               before. 

Second 
before. 

Mean  for 
A  a. 

V.syt 

I           . 

6. 45 

11.                       15.55 

20.2 

4.58  nn. 

Kx,.t. 

-» 

6.55 

10.95               15.5 

20.1 

4.53  .111. 

Lxit, 

J-    • 

■,     "■=      1 

10.97               15.53 

i 

20.17 

1 

4.55  nil. 

1 

and  tliL-  mean  of  these  j^nves  /./2  =  4.-,6  cm.  to  witliin  a  fi-action  of 
one  pel- cent.  The  vibrator  con.sisted  of  two  .spheres  1.93  cm.  in 
diameter  arraiiijed  as  in  l*"ig.  I . 

5.    K.STIMATION    OK    "  (V ." 

II  we  accept  the  theory  gi\'en  on  pat^e  5  as  correct  we  can  from 
the  curve  find  the  logaritlimic  decrement  of  the  vibrator.  Let  t^^,  a.,, 
<?.,,  be  readings  for  .r=o=//4  and  //2  respectively,  then 


«/  =0=2  lOLT 

Now  the  first  minimum  and  maximum  of  the  curve  (i)  correspond 
nearly  with  the  values  of  .r=^,/4  and  )./2  respectivelj-.  Using  these 
values  in  the  curve  (i)  we  get,  since  r7,=  i4.5,   '^2=l-2i^    '^.■.=9-^> 

5=0.74. 

But  it  is  certain  that  this  theor\-,  though  it  may  apply  when  re- 
ceivers are  used  which  are  dead  beat  compared  with  the  vibrators, 
docs  not  apply  in  the  case  of  Klemencic  and  Czarmak's  experiments 
nor  in  our  own  ;  for  we  have  found  that  the  interference  curve  is  in- 
fluenced by  the  receiver — a  fact  which  this  theory  neglects.  How- 
ever, it  is  interesting  to  compare  the  values  of  2  log     '       ■   (w  hich 

we  will  call  o'  and  which  has  some  connection  with  the  damping  of 
the  \ibrator  or  receiver  or  both),  found  by  Klemencic  and  Czarmak 
and  others,  for  Hertzian  vibrators  and  receivers,  with  the  correspond- 
ing value  for  the  spheres  and  coherer.  Their  values  varied  from 
0.3  to  0.5  while  ours  varied  from  0.5  to  i.  This  indicates  either  a 
more  complex  radiation  or  a  higher  damping  coefficient  in  the  case 
of  our  apparatus  than  in  that  of  the  earlier  experiment.     But  these 


Nm,  4.] 


C  ■.VA   ( >/■   A\'/"/;A7  A  A'( M/A  / AA'. 


I  I 


values  (0.5  to  0  ■'ii'c  coiisidcrabl)-  lower  tliaii  that  sui;L;cstr(l  by 
theory.  I'or  the  aniphtmle  oftlie  oscilIali<ins  produced  1j)-  the  dis- 
turbance of  a  distrilnition  of  electricity  on  a  spiiere  is   where  (?  =  ra- 


dius  of  the  spliere,  =<' 


()=  '     '/'  =  /./2<r.      In  thi 
1/1  ' 


case  of  this  vilirator  ^7=  i  nearly  and  /=9. +  .  hence  ''  =  4.5.  This, 
however,  is  the  case  of  an  isohited  sphere,  a  condition  wiiich  dues 
not  exist  in  our  eNperinient.  Hut  in  hiter  work  we  used  one  spiiere 
and  a  small  knob  spari<in<,f  to  it  and  the  value  of  did  not  exceed 
the  value  l  .0.  Hence  it  ai)pears  either  that  iV  is  not  eipial  to  (1  or 
that  Tiionison's  theory  does  not  a^n'ee  with  experiment.' 

6.   IxriXKNCK  or  Rixkivkk  lpon  tiik  iMr.KrKKi'.NCK  Clkvk. 

So  far  nothin^r  has  been  said  rei;ardin.t:j  the  wave-length  iiieasureil 
as  to  whether -it  is  that  of  the  vibrator  or  is  due  to  a  property  of  the 
receiver.  It  seemetl  that  the  i)eriod  of  the  latter  nut^dit  depend  :  on 
(l)  the  dimeiisions  and  arrauL^enient  of  the  nails  ;  (2)  the  dimensions 
of  the  tube.  In  order  to  vary  these  (piantities  three  other  receivers 
were  used.  In  receiver  II  there  were  nails  like  those  in  receiver  I, 
but  the  tube  and  terminals  were  different.  Receiver  III  had  in 
place  of  nails,  copper  wire  cut  up  into  lengths  varying  from  2  mm. 
to  2  cm.  In  receiver  IV  were  used  steel  spheres  about  4  mm.  in 
diameter.  Two  vibrators  were  used.  No.  I  already  referred  to  and 
No.  2,  which  differed  from  it  only  in  having  spheres  .93  cm.  in 
diameter.  The  interference  curves  are  given  in  Mg.  2.  If  the  re- 
ceiver exerci-sed  no  influence  on  the  interference  curve  the  curves  i, 
3,  5,  7,  should  be  similar,  as  also  should  2,  4,  6,  8.  We  reach, 
therefore,  a  very  definite  conclusion,  the  interference  curve  depends 
partly  on  the  receiver. 

In  the  curves  i,  3,  5,  7,  we  notice  that  /  has  approximately  the 
value  9.2  cm.  This  value  then  we  take  to  be  the  wave-length  of  the 
radiation  from  vibrator  I. 

The  curve  (No.  2)  for  vibrator  2  and  rect^iver  i  was  obser\'ed 
many  times  and  it  always  assumed  forms  between  the  dott-xl  and 
continuous  lines  of  No.  2.  It  seems  due  to  two  components,  one 
of  wave-length  8.6  cm.  and  the  other  of  half  that  wave-length.      In 

I  J.  J.  Thompson,  "  Recent  Researches,"  p.  370. 


la 


2a 


/ 

\i //        ^ 

;    :     :    1    1    1     1    !     1    1     1    1    1    1 

1   1    i   1   1   '    >   ;   ;   ,. 

u— 

r>  -• 

0  — 


.J- 


I  I  I  I 


I   .  I   I   I  I   !   I  I    I  1  :   !   ^   I   I  I 


I   I   I    I    I   I    M   I    I    I   I    '   I    I   I    '    I    '!    I 


I   I   I   I  I   I    I  I   I   I   I 


I   I    '   I   I   I   I   I    I   I   I 


I   I   .   '    '  I   ' 


Fig.  2. 


V^ 


N...  4.] 


r.s/-;  ('/■'  /.\7y;A7'7;A'('.i//;yA7v'. 


I  ; 


view  of  tlie  fact  that  receivers  11  ami  111  f'rthis  vibrator  -ave  a 
\vave-leni;lh  («f  4. J  to  4.4  cm.,  we  arc  led  to  believe  that  the  com- 
ponent of  the  shorter  \vave-leiii;th  is  due  to  the  \  ibrator  and  that 
the  other  component,  which  is  present  probably  to  a  sliL;ht  extent 
in  the  radiator,  owes  its  prominence  to  a  resonance  action  of  the 
receiver.  The  interpretation  that  receiver  1  has  a  period  correspond- 
in-r  to  the  ion"-  wave  receives  confn-mation  in  the  fact  that  the  cnrvc 
for  vibrator  1  has  such  well  defined  maxima  and  minima.  Hut, 
\vhate\er  interpretation  be  placed  on  the  interference  cur\e,  it  is 
evident  that  it  cannot  always  be  taken  to  accurately  represent  the 
radiation.  On  the  other  hand  the  wave-len|^th  for  either  vibrator  is 
maintainetl  by  all  the  receivers  (leavini;  out  curcvs  6,  7,  8,  for 
which  the  wave-lengths  are  very  indehnite).  This  fact  shows  that 
our  receiver  has  far  less  influence  on  the  interference  curve  than  has 
the  Hertzian  receiver.  In  other  wiuxls,  the  damping  coefficient  of 
the  former  is  far  less  greater  than  that  of  the  latter.  Our  expecta- 
tion, therefore,  that  the  coherer  used  is  highly  dami)eil  has  been 
fulfilled,  but  it  appears  from  our  work  that  its  damping  coefficient 
is  of  the  same  order  of  magnitude  as  that  of  the  vibrator  and  con.se- 
quently  it  influences  the  interference  curve. 

In  view  of  this  action  of  the  receiver  we  are  not  able  to  accurately 
analyze  the  radiation,  but  using  a  number  of  receivers  we  are  able 
to  arrive  at  a  fair  estimate  of  its  nature.  We  are  thus  led  to  state 
that  the  chief  component  of  the  radiation  from  spheres  is  due  to  a 
damped  oscillation. 

7.    DeFENDEN'CE  of  /  II'ON  VlI!K.\T()K. 

Besides  the  vibrators  i  and  2  we  used  the  following  arrange- 
ments :  Vibrator  No.  3,  consi.sting  of  one  sphere  of  No.  i,  to 
which  sparked  a  small  platinum  bead.  The  interference  curve  is 
given  in  No.  i„.  The  wave-length  is  the  same  as  that  of  No.  i, 
but  the  maxima  and  minima  are  less  pronounced.  Vibrator  4  dif- 
fered from  No.  3  only  in  having  one  of  the  spheres  of  vibrator  2  in 
place  of  one  from  No.  i.  The  interference  curve  is  that  of  2,,. 
Here  again  the  wave-length  is  the  same  as  when  the  two  spheres 
arc  used.  We  also  used  two  steel  spheres  0.79  cm.  in  diameter 
together  and  singly.     Their  curves,  which  are  similar  to  those  al- 


H 


c.  /•;  //i/.L. 


[Vmi..  V 


!■  ^^■ 


read)-  found,  arc  not  ■;iv(.ii.  The  wavc-lcn^^tli  was  a'xmt  4  cm. 
Rij;Iii's  form  of  vibrator,  with  the  two  sj)licrc.s  of  No.  I  sparking'  in 
oil  and  tho.sc  of  No.  2  .sparkinj^f  in  air,  \va.s  nseil.  The  waw-len^^th 
wa.s  a^^ain  ai)])ro\imatel\'  efpial  to  that  of  No.   i. 

It  is  here  seen  tliat  tlie  wave-len^'th  is  nearl\'  proportional  to  the 
diameter  of  the  sphere  (the  law  is  e.xpressed  more  nearl)-  by 
/.  =  ///(^r+(i)  where  ///  and  o  are  constants  and  /•=  railius  of  the 
.sphere),  and  that  it  is  indeiiendent  of  the  arran^fenienl  b>'  means  of 
which  the  tlischar{;e  is  broujjjht  about.  1  was  not  able  to  observe 
anj-  change  of  wave-lenj;th  due  to  a  change  of  sparkling  distance. 
It  is  iiUerestins.'  to  compare  the  values  of  /  obtained  by  other  ob- 
servers with  those  which  we  have  found.  It  will  be  seen  that  no 
aL;reement  exists  between  the  results  of  any  two  observers. 


Dia.  of 
Spheres. 

mm. 
39.7 
24.4 
10.6 


lfr^rwr^'ATor\      ^"-ver.       M.V;?^^°f     Observer.  Reference. 


nun, 

88       I     Kighi'.s 

82 

80 


80. 

200 

37.  S 

106 

8. 

26 

7.8 

18.4 

19.3 

91 

9.3 

43 

7.9 

40 

I.LMl(,'th  of 

ivliiulcr. 

8x1  mm. 

SO 

1.3x0.5  " 

6 

Nail  I                     I 

Coherer.  Interference  l.anj;. 

"  througli     ,  " 

"  two  tubes.  " 


Kiglii's         Sliver  on      Interference      Rigiii. 
"  Glass.  .Spark  "  " 

"  j  Ohservcd.  "  '         " 


18.4  Lodge's  one  Siiirnl  spring  Grating.     \      lk).se. 

Sphere,     j    Coherer.  j 

Righi's  and    Coherers.  Interferom- 

Lodge's.    ,  eter. 


Righi's 


Thermo- 
element. 


Cole. 


Interference  Lebedew 


AVied.    Ann.,    3, 
I     1896. 

l.'eclair.age  Llee- 
trique.  Xo.  3, 
p.  360.    1S95. 

llVoe.   Koy.   .Soc, 
j     I.X,  361,  1S96. 

jSee  pages  13-16. 


Physical   Review. 

1S96. 
Wicd.  Ann. 

No.  9,   1895. 


Surely  but  one  interpretation  can  be  placed  upon  the  values  of/ 
as  found  by  Lang.  It  is  that  th.e  wave-length  measured  is  due 
chiefly  to  the  receiver. 

8.  Determination  of  /x. 

In  order  to  determine  accurately  the  index  of  refraction  of  a 
medium  transparent  to  electric   waves   by  the  interferometer  it  is 


No.  4] 


IS/:  VI-  IXri.HllKoMl.lhK. 


15 


necessary  that  uv  have  an  iiUrrtrriin\  (.iirvr  with  urll  dirmcd 
maxima  and  miiiiina.  The  iiilliitnce  ot'  tlie  irci'ivir  011  tlii>.tiir\c 
is,  of  coursi-,  a  iiialUr  of  no  i-oikl';ii  except  that  it  ^houlil  assist  in 
^'ivin;^r  this  ileilnitioii.  Neither  docs  th.e  ([iiestion  of  tlie  iiaturi'  ol 
the  r.idiation  concern  us  unless  (wliat  is  exceeth'n^dy  iniprohahU) 
the  medium  in  (|uestion  exercisi's  siKetiw;  absorption  li)r  the-^e  Iim^^' 
wa\cs. 

To  prewnt  the  radiation  uliieli  is  reflected  from  tlie  surf  ices  of 
the  plate  from  reachiii<;  the  receiver,  the  j)l.ite  should  he  inclined  .it 
an  aULjle  to  the  ra\'s.  If  the  index  of  refraction  is  not  much 
greater  than  unity,  tiiis  ])rec.iution  is  uiuucessary.  If,  however,  the 
plate  is  kept  normal  to  the  rays,  its  thickness  should  he  varied 
gradually  tiir()UL;h  at  least  a  wave-lenL;th  and  the  mean  of  all  the 
results  taken.' 

In  oriler  to  find  the  ile;j;ree  of  accurac)'  with  which  the  value  of// 
may  be  determined  by  this  method,  obserxations  were  ma<le  with  a 
block  of  wood  8.2  cm.  thick.  The  displacements  of  the  first  and 
sccoml  minima  on  both  sides  of  the  zero  ixisition,  and  with  the  block 
before  either  mirror  were  found.  UsiiiL;  the  formula  ii.  =  (i/-\-i))  /d 
the  following  si.x  values  were  obtained:  1.87,  1.80,  1.86,  1.83, 
1.88,  1.83;  giving  a  mean  of  1.845  witli  a  mean  scpiare  error  of 
0.027.  In  these  observations  the  fibres  of  the  wootl  were  horizontal. 
When  the  fibres  were  vertical  the  values  2.03,  2. 01  were  found. 
These  results  are  sufficient  to  show  (i)  that  the  error  in  determin- 
ing n  need  not  exceed  one  per  cent.,  (2)  that  the  wood  useil  is 
doubly  refracting. 

Concliiswit. — The  points  of  difference  between  light  and  electric 
radiation  whicli  have  been  noticed  in  i(2  tend  to  make  the  problem 
of  the  analysis  of  the  radiation  more  difficult  in  the  case  of  electricity 
than  in  that  of  light.  For  there  are  added  to  the  variables  of  the 
vibrator  those  of  the  receiver.  However,  when  we  find  that  there 
is   present  in  all  the  interference  cur\'es  for  one  vibrator  a  certain 

'  I'hij  (iiily  theory  which  appe.irs  to  us  to  apply  is  complicated  ami  will  not  assist  us. 
The  action  on  the  receiver  is  given  liy 

V<,U>{t)Ydt\-  r    [o(/')  +  /'(/)]V/  where  l\t)  is  found 

by  taking  account  of  the  radiation  rellected  successively  from  tlie  surfaces  of  the  plate. 
This  itself  is  a  complicated  expression. 


i6 


(,-.  /•  mil.. 


[V,.|,  V. 


iKiiu  III  wi  arc  -^ali'  in  ^.i)  iiil;  lli.it  tliat  i  K  iiKiil  i->  diir  to  an  loiilLi- 
ticii  ut'  a  iliTinitf  iRTi<ul  nii  tlir  vibiator.  Wc  aiv  iidt  justitlctl  at 
present  in  U"''"k'  Imtlu  r  tliaii  this. 

'I'lic  rulliiwiii^;  arc  llu'  iniu  Iiisiuim  at  uhiili  uc  .irrivL' : 

I.  riir  intcTtirriKH'  ciir\<s  di'iniiil  lui  l)iitli  tlu'  \il)rator  anil 
rcciiw  r. 

J.    riir  mlliKiicc  of  each  nl'tlu'^r  \,irics. 

^.  I  he  l<i;4aritlimic  flicivnn  nt  (it'thc  rcc'ji\er  is  ot'tlic  saiiic  unlcr 
ot"  nia;4nitiul(j  as  that  nfthi'  vibrator. 

\.  IIr'  chirf  comiHuunt  ot'  tlic  radiation  and  the  ]K'n"n(I  of  tlio 
vil)iator  may  Ik;  ditirniiiicd  from  a  number  of  interference  curves, 

5.  I'liis  receiver  coiiM  be  used  to  anal\/.e  tlie  radiation  where 
tile  osciUalions  are  but  sh^htly  damped. 

6.  The  error  in  ilelermininj,'  the  index  of  lefraction  need  not 
exceed  one  per  cent. 

7.  Progress  is  to  be  looked  for  in  obtaining  :  (r?)  a  more  constant 
source  ;  (/')  a  more  constant,  dead  beat,  \'et  sensitive  receiver. 

This  research  was  carried  on  at  the  Ryerson  I'ln'sical  Laboratory 
under  the  direction  of  lleail  Professor  A.  A.  Michelson,  to  whom 
as  also  to  associate  Professor  Stratton,  I  am  indebteil  for  many  su^;- 
j^cstions  and  much  encouragement. 

KVI  K'MiN    I'llV^Ii  Al    I.M'iil;  MiiKV, 

l'M\IK>riY  01    (■llir\(,(i,  May  I,  I.Si)7. 


w 


\ 


^r  JB.5  lyoi 


1,1- 

at 


tlu- 

icrc 

not 

ant 

oiy 
om 
II-:- 


The  Physical  Review. 

A  'Journal  of  Experimental  and  Theoretical  Physics, 

CONDUCTRD  BY 
EDWARD    L.   NICHOLS,    ERNEST    MERRITT  and    FREDERICK    BEDELL. 


XXVI.    Auffust,  1897. 

TABU  OF  COHTBMTS. 
FnmttopiM*. 

Ob  tlM  CoHTtnlon  of  BlMtrlo  Bawgy  in  Dlctoetriet.    in.    Richard  THRiLrAix. 
A  Dttwmliutkm  of  tho  SpoeUe  SMttUaoo  uA  Tomporaton  CotlBclaBt  of  Oil  la 
Thin  rUna,  and  the  Application  of  thaao  Katolta  to  the  Meaaurement  of  the 
Thlckneaa  of  the  OU  Film  In  Joomal  Bona.    F.  L.  O.  Waoswohth. 
Certain  Pnpertlea  of  Beat  Warea  of  Great  Waye-Length.    I.    H.  Rubens  and 

E.  F.  NiCHOU. 
Minor  Contribution :  On  the  Relation  Between  the  Onnotic  Preaure  and  the  Vapor 

Premre  of  Solntioni.    A.  A.  Ntytt  and  C.  G.  Aiiett 
Vote :  Alfrad  ManhaU  Mayer 

Hew  Booka:  T.  W.  WrffAt:  Elements  of  Mechanics,  y.  S.  Amti.-  Theory  of 
Physics.  IV.  Ackrcyd:  The  Old  Light  and  the  New.  E.  P.  Thompson  and 
tV.  A.  AntAony.-  Roentgen  Rays  and  Phenomena  of  the  Anode  and  Cathode. 
'AT.  J.  Morton:  The  XRay  or  the  Photography  of  the  Inrisible.  Giorgtt 
Vitomx:  Les  Rayons  X  et  U  Photographle  de  I'lnrisible. 


XXVII.    September,  1897. 

TABU  OF  COHTBBTS. 

Are  Spectra.    Arthur  L.  Foley. 

Certain  Propertlea  of  HMt  WaToo  of  Oroat  WaTo-Ieagth.    n.    H.  Rubens  and 
E.  F.  Nichols. 

The  Snrfaoe  Tenaioa  of  Water  and  of  Certain  Dilate  Aqnaona  Solatloaa,  I>eter> 
mined  by  the  Method  of  Klpplea.    I.    N.  Ernest  Dorsby. 

Minor  CoatrlbatlOB:  A  New  Method  of  Determining  the  Specific  Heats  of  Liquids. 
Robert  L.  LUek. 

New  Bottka:  IV.  A.  Stont:  Experimental  Physics.  A.  E.  DoUtar:  First  Principles 
of  Natural  Philosophy.  C.  P.  Sttinmttt :  Alternating  Current  Phenomena.  A.  C. 
Crthore  and  G.  O,  Sfuitr:  A  Polarizing  Photochronograph.  E.  Mack:  Contri- 
bution to  the  Analy^  of  the  Sensations  (transUted  by  C  M.  Williams). 
Adams  :  Scientific  PRpeis  of  John  Couch  Adams. 


W.G, 


PUBLISHED  FOR  CORNELL  UNIVERSITY. 
THE  MACMILLAN  COMPANY  -  -  -  NEW  YORK. 


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